Ester-free synthetic lubricating oils comprising polybutenyl substituted succinic acid or anhydride and hydrocarbon polymer

ABSTRACT

Synthetic lubricating oils for use in lubricating internal combustion engines, having good compatibility with elastomeric seals and good stability, but without making use of organic acid ester basestocks, comprise a synthetic basestock such as polyalphaolefin oligomers, an additive package comprising a hydrocarbyl substituted dicarboxylic acid or anhydride in which the hydrocarbyl group has a number average molecular weight (M n ) of from 700 to 5000 and a viscosity modifier.

This invention relates to synthetic lubricating oils for use inlubricating internal combustion engines, having good compatibility withelastomeric seals and good stability.

Multigrade lubricating oils typically are identified by designationssuch as SAE 10W-30, 5W-30 etc. The first number in the multigradedesignation is associated with a maximum low temperature (e.g., -20° C.)viscosity requirement for that multigrade oil as measured typically by acold cranking simulator (CCS) under high shear rates (ASTM D5293, whichis a revision of ASTM D2602), while the second number in the multigradedesignation is associated with a high temperature viscosity requirementusually measured in terms of the kinematic viscosity (kV) at 100° C.(ASTM D445). Thus, each particular multigrade oil must simultaneouslymeet both strict low and high temperature viscosity requirements, sete.g. by SAE specifications such as SAE J300, in order to qualify for agiven multigrade oil designation.

The high temperature viscosity requirement is intended to prevent theoil from thinning out too much during engine operation which can lead toexcessive wear and oil consumption. The maximum low temperatureviscosity requirement is intended to facilitate engine starting in coldweather. Reduced low temperature viscosity will also help to ensurepumpability, i.e., the cold oil should readily flow to the oil pump,otherwise the engine can be damaged due to insufficient lubrication.

The viscosity characteristic of a basestock on which a lubricating oilis based is typically expressed by the neutral number of the oil (e.g.,S150N) with a higher neutral number being associated with a higherviscosity at a given temperature. Blending basestocks is one way ofmodifying the viscosity properties of the resulting lubricating oil. Thebasestocks which are typically used in lubricating oils may be syntheticor natural oils. Unfortunately, merely blending basestocks of differentviscosity characteristics may not enable the formulator to meet the lowand high temperature viscosity requirements of some multigrade oils. Theformulator's primary tool for achieving this goal is an additiveconventionally referred to as a viscosity modifier (VM) or viscosityindex improver (V.I. improver).

A monofunctional VM is conventionally an oil-soluble long chain polymer.A multifunctional VM (or alternately MFVM) is an oil soluble polymerwhich has been chemically modified e.g., functionalized and derivatized,to impart dispersancy as well as viscosity modification.

For multigrade oils to meet the high temperature viscosity requirements,it is often necessary to add significant amounts of VM which in turnresults in increased low temperature viscosity. In order to meet therequirements for wide multigrades such as SAE 5W-20, 5W-30, 10W40,10W-50, 15W-40 and 15W-50, it is usual to reduce the basestock viscosityby blending in less viscous oils--i.e. to lower the average neutralnumber of the total basestock. If conventional mineral basestocks areused it is usual to replace higher viscosity basestocks such as 600Nbasestock in part by basestock of 150N or less to improve CCSperformance in wide multigrades. This results in the formulated oilbecoming more volatile which may in turn increase oil consumption.

An alternative means of reducing the basestock viscosity and thereforeimproving CCS performance is to employ so-called non-conventionallubricants (or NCL). Examples of NCLs are synthetic basestocks such aspolyalphaolefin oligomers (PAO) and diesters and specially processedmineral basestocks such as basestocks, waxes or other heavy fractionswhich are hydrocracked or hydroisomerised to give greater paraffiniccontent and lower aromatic content.

The American Petroleum Institute (API) in their Publication 1509 datedJanuary 1993, amended as of Jan. 1st 1995, entitled "Engine OilLicensing and Certification System" (EOLCS) in Appendix E, 1.2 provideda classification of basestocks in 5 categories, which are widely used inthe lubricant industry. Conventional mineral basestocks are in Groups 1and 2; NCLs are basestocks that do not fall within those two Groups.

In addition increasingly severe performance requirements for lubricantsas well as environmental considerations has lead to increasing use ofsynthetic basestocks, to the extent of lubricants becoming fullysynthetic--i.e., using only synthetic basestocks. However, suchsynthetic lubricants have not previously been formulated withpolyalphaolefin oligomers as the basestock without ester basestocksbeing used in addition to provide seal compatibility, particularly withfluorocarbon seals, and adequate solubility of the additives used toformulate the lubricants. Inadequate additive solubility in thebasestock gives rise to problems of stability with additives tending tofall out of solution on storage, which is clearly unacceptable.Synthetic ester basestocks have drawbacks--for example, they may giverise to excessive wear of valve train components.

Additives which enhance the seal compatibility of conventionallubricants are known. U.S. Pat. No. 4,940,552 and Research Disclosures,May 1992, No. 337, page 348 describe the use of dicarboxylic acidanhydrides for this purpose but there is no indication of how theproblem is addressed in fully synthetic lubricants, or any mention ofdealing with solubility issues in synthetic basestocks.

Thus, in one aspect the invention provides a synthetic lubricating oilfor an internal combustion engine which comprises:

a. a synthetic basestock of lubricating oil viscosity substantially freeof both natural oils and synthetic organic acid ester oils;

b. an additive package comprising a hydrocarbyl substituted dicarboxylicacid or anhydride in which the hydrocarbyl group has a number averagemolecular weight (M_(n)) of from 700 to 5000; and

c. a viscosity modifier.

DETAILED DESCRIPTION

A. Basestock

The basestock used in the lubricating oil of the invention comprisessynthetic oils other than ester oils, and is substantially free ofnatural oils so that the lubricating oil may be described as fullysynthetic.

Additives used in formulating lubricating oils often contain diluentoil; this diluent oil introduced with additives is not included withinthe term "basestock" as that term is used herein, which is confined tothe oil used to dilute the additives to form the finished lubricatingoil. Thus, it is not excluded that the lubricating oils may containsmall amounts of natural oils introduced in the form of such diluents,but typically the amounts of such natural diluent oils will amount to nomore than 18% by weight of the finished lubricating oil.

The lubricating oil basestock conveniently has a viscosity of from 2.5to 12 mm² /s, and preferably from 2.5 to 9 mm² /s, at 100° C.Non-organic-acid-ester synthetic basestocks include chlorofluorocarbonpolymers, silicones, silicate esters, fluoresters and polyphenyl ethers,but polyalphaolefin oligomers (PAO) are particularly preferred.Commercially available PAO basestocks of this type include: SHF 41, 61and 82 available from Mobil Corporation, Synfluid 2, 4 and 6 availablefrom Oronite and Durasyn 106 and 164 available from AlbemarleCorporation.

B. Additive Package

1. Hydrocarbyl Substituted Dicarboxylic Acid or Abhydride

The additive package used in the invention comprises the additives whichprovide the desired performance characteristics for the finishedlubricating oil. The invention requires that this package contain ahydrocarbyl substituted dicarboxylic acid or anhydride in which thehydrocarbyl group has a number average molecular weight (M_(n)) of from700 to 5000.

The hydrocarbyl group is typically an olefin polymer, especially apolymer comprising a major molar amount (i.e. greater than 50 mole %) ofa C₂ to C₁₈ olefin (e.g., ethylene, propylene, butylene, isobutylene,pentene, octene-1, styrene), and typically a C₂ to C₅ olefin. The oilsoluble polymeric hydrocarbon backbone may be a homopolymer (e.g.polypropylene or polyisobutylene) or a copolymer of two or more of sucholefins (e.g. copolymers of ethylene and an alpha-olefin such aspropylene and butylene or copolymers of two different alpha-olefins).Other copolymers include those in which a minor molar amount of thecopolymer monomers, e.g., 1 to 10 mole %, is a C₃ to C₂₂ non-conjugateddiolefin (e.g., a copolymer of isobutylene and butadiene, or a copolymerof ethylene, propylene and 1,4-hexadiene or 5-ethylidene-2-norbornene).

One preferred class of olefin polymers is polybutenes and specificallypolyisobutenes (PIB) or poly-n-butenes, such as may be prepared bypolymerization of a C₄ refinery stream.

Another preferred class of olefin polymers is ethylene alpha-olefin(EAO) copolymers or alpha-olefin homo- and copolymers having in eachcase a high degree (e.g. >30%) of terminal vinylidene unsaturation. Thatis, the polymer has the structure: P-HCR=CH₂ wherein P is the polymerchain and R is a C₁ -C₁₈ alkyl group, typically methyl or ethyl.Preferably the polymers have at least 50% of the polymer chains withterminal vinylidene unsaturation. EAO copolymers of this type preferablycontain 1 to 50 wt. % ethylene, and more preferably 5 to 45 wt. %ethylene. Such polymers may contain more than one alpha-olefin and maycontain one or more C₃ to C₂₂ diolefins. Also usable are mixtures ofEAO's of low ethylene content with EAO's of high ethylene content. TheEAO's may also be mixed or blended with PIB's of various M_(n) 's orcomponents derived from these may be mixed or blended. Atactic propyleneoligomer typically having M_(n) of from 700 to 500 may also be used, asdescribed in EP-A-490454.

Suitable olefin polymers and copolymers, such as polyisobutenes, may beprepared by cationic polymerization of hydrocarbon feedstreams, usuallyC₃ -C₅, in the presence of a strong Lewis acid catalyst and a reactionpromoter, usually an organoaluminum such as HCl or ethylaluminumdichloride. Tubular or stirred reactors may be used. Suchpolymerizations and catalysts are described, e.g., in U.S. Pat. Nos.4,935,576 and 4,952,739. Fixed bed catalyst systems may also be used asin U.S. Pat. No. 4,982,045 and UK-A 2,001,662. Most commonly,polyisobutylene polymers are derived from Raffinate I refineryfeedstreams. Conventional Ziegler-Natta polymerization may also beemployed to provide olefin polymers suitable for use to preparedispersants and other additives.

The preferred EAO polymers may be prepared by polymerizing theappropriate monomers in the presence of a catalyst system comprising atleast one metallocene (e.g. a cyclopentadienyl-transition metalcompound) and preferably an activator, e.g. an alumoxane compound. Themetallocenes may be formed with one, two, or more cyclopentadienylgroups, which are substituted or unsubstituted. The metallocene may alsocontain a further displaceable ligand, preferably displaced by acocatalyst--a leaving group--that is usually selected from a widevariety of hydrocarbyl groups and halogens. Optionally there is a bridgebetween the cyclopentadienyl groups and/or leaving group and/ortransition metal, which may comprise one or more of a carbon, germanium,silicon, phosphorus or nitrogen atom-containing radical. The transitionmetal may be a Group IV, V or VI transition metal. Such polymerizationsand catalysts are described, for example, in U.S. Pat Nos. 4,871,705,4,937,299, 5,017,714, 5,120,867, 4,665,208, 5,153,157, 5,198,401,5,241,025, 5,057,475, 5,096,867, 5,055,438, 5,227,440, 5,064,802;EP-A-129368, 520732, 277003, 277004, 420436; WO91/04257, 93/08221,93/08199 and 94/13715.

The M_(n) for such polymers can be determined by several knowntechniques. A convenient method for such determination is by gelpermeation chromatography (GPC) which additionally provides molecularweight distribution information, see W. W. Yau, J. J. Kirkland and D. D.Bly, "Modern Size Exclusion Liquid Chromatography", John Wiley and Sons,New York, 1979.

The dicarboxylic acid or anhydride is preferably a succinic acid oranhydride. These preferred products may be prepared by knownfunctionalisation reactions which include: halogenation of the polymerat an olefinic bond and subsequent reaction of the halogenated polymerwith maleic acid or anhydride; and reaction of the polymer with maleicacid or anhydride by the "ene" reaction absent halogenation.Particularly preferred succinic anhydrides are those with apolyisobutenyl backbone, typically having an M_(n) of from 700 to 2500,for example 900 to 1100.

The dicarboxylic acid or anhydride is typically used in the additivepackage in an amount such that it is present in the finished oil in anamount of from 0.01 to 5 mass %. Preferably it is used in an amountcorresponding to it being present in the oil in an amount of from 0.1 to1 mass %.

Additional additives present in the additive package typically includeashless dispersants, metal or ash-containing detergents, antioxidants,anti-wear agents, friction modifiers, rust inhibitors, anti-foamingagents, demulsifiers, and pour point depressants.

2. Ashless Dispersant

The ashless dispersant comprises an oil soluble polymeric hydrocarbonbackbone having functional groups that are capable of associating withparticles to be dispersed. Typically, the dispersants comprise amine,alcohol, amide, or ester polar moieties attached to the polymer backboneoften via a bridging group. The ashless dispersant may be, for example,selected from oil soluble salts, esters, amino-esters, amides, imides,and oxazolines of long chain hydrocarbon substituted mono anddicarboxylic acids or their anhydrides; thiocarboxylate derivatives oflong chain hydrocarbons; long chain aliphatic hydrocarbons having apolyamine attached directly thereto; and Mannich condensation productsformed by condensing a long chain substituted phenol with formaldehydeand polyalkylene polyamine.

The oil soluble polymeric hydrocarbon backbone is typically an olfinpolymer as described above, and will usually have number averagemolecular weight (M_(n)) within the range of from 300 to 20,000. TheM_(n) of the backbone is preferably within the range of 500 to 10,000,more preferably 700 to 5,000 where the use of the backbone is to preparea component having the primary function of dispersancy. Hetero polymerssuch as polyepoxides are also usable to prepare components. Bothrelatively low molecular weight (M_(n) 500 to 1500) and relatively highmolecular weight (M_(n) 1500 to 5,000 or greater) polymers are useful tomake dispersants. Particularly useful olefin polymers for use indispersants have M_(n) within the range of from 1500 to 3000.

The oil soluble polymeric hydrocarbon backbone may be functionalized toincorporate a functional group into the backbone of the polymer, or aspendant groups from the polymer backbone. The functional group typicallywill be polar and contain one or more hetero atoms such as P, O, S, N,halogen, or boron. It can be attached to a saturated hydrocarbon part ofthe oil soluble polymeric hydrocarbon backbone via substitutionreactions or to an olefinic portion via addition or cycloadditionreactions. Alternatively, the functional group can be incorporated intothe polymer by oxidation or cleavage of a small portion of the end ofthe polymer (e.g., as in ozonolysis).

Useful functionalization reactions include: halogenation of the polymerat an olefinic bond and subsequent reaction of the halogenated polymerwith an ethylenically unsaturated functional compound; reaction of thepolymer with an unsaturated functional compound by the "ene" reactionabsent halogenation (an example of the former functionalization ismaleation where the polymer is reacted with maleic acid or anhydride);reaction of the polymer with at least one phenol group (this permitsderivatization in a Mannich Base-type condensation); reaction of thepolymer at a point of unsaturation with carbon monoxide using aKoch-type reaction to introduce a carbonyl group in an iso or neoposition; reaction of the polymer with the functionalizing compound byfree radical addition using a free radical catalyst; reaction with athiocarboxylic acid derivative; and reaction of the polymer by airoxidation methods, epoxidation, chloroamination, or ozonolysis.

The functionalized oil soluble polymeric hydrocarbon backbone is thenfurther derivatized with a nucleophilic amine, amino-alcohol, or mixturethereof to form oil soluble salts, amides, imides, amino-esters, andoxazolines. Useful amine compounds include hydrocarbyl amines or may bepredominantly hydrocarbyl amines in which the hydrocarbyl group includesother groups, e.g., hydroxy groups, alkoxy groups, amide groups,nitriles, imidazoline groups, and the like. Particularly useful aminecompounds include mono- and polyamines, e.g. polyalkylene andpolyoxyalkylene polyamines of about 2 to 60, conveniently 2 to 40 (e.g.,3 to 20), total carbon atoms and about 1 to 12, conveniently 3 to 12,and preferably 3 to 9 nitrogen atoms in the molecule. Mixtures of aminecompounds may advantageously be used such as those prepared by reactionof alkylene dihalide with ammonia. Preferred amines are aliphaticsaturated amines, including, e.g., 1,2-diaminoethane;1,3-diaminopropane; 1,4-diaminobutane; 1,6-diaminohexane; polyethyleneamines such as diethylene triamine; triethylene tetramine; tetraethylenepentamine; and polypropyleneamines such as 1,2-propylene diamine; anddi-(1,2-propylene)triamine.

Other useful amine compounds include: alicyclic diamines such as1,4-di(aminomethyl)cyclohexane, and heterocyclic nitrogen compounds suchas imidazolines. A particularly useful class of amines are the polyamidoand related amido-amines as disclosed in U.S. Pat. Nos. 4,857,217;4,956,107; 4,963,275; and 5,229,022. Also usable istris(hydroxymethyl)amino methane (THAM) as described in U.S. Pat. Nos.4,102,798; 4,113,639; 4,116,876; and UK 989,409. Dendrimers, star-likeamines, and comb-structure amines may also be used. Similarly, one mayuse the condensed amines disclosed in U.S. Pat. No. 5,053,152. Thefunctionalized polymer is reacted with the amine compound according toconventional techniques as described in EP-A 208,560; U.S. Pat. No.4,234,435 and U.S. Pat. No. 5,229,022.

A preferred group of nitrogen containing ashless dispersants includesthose derived from polyisobutylene substituted with succinic anhydridegroups and reacted with polyethylene amines (e.g. tetraethylenepentamine, pentaethylene, polyoxypropylene diamine) aminoalcohols suchas trismethylolaminomethane and optionally additional reactants such asalcohols and reactive metals e.g. pentaerythritol, and combinationsthereof).

Also useful as nitrogen containing ashless dispersants are dispersantswherein a polyamine is attached directly to the long chain aliphatichydrocarbon as shown in U.S. Pat. Nos. 3,275,554 and 3,565,804 where ahalogen group on a halogenated hydrocarbon is displaced with variousalkylene polyamines. Another class of nitrogen-containing is ashlessdispersants comprises Mannich base condensation products. Such Mannichcondensation products may include a long chain, high molecular weighthydrocarbon (e.g., M_(n) of 1,500 or greater) on the benzene group ormay be reacted with a compound containing such a hydrocarbon, forexample, polyalkenyl succinic anhydride as shown in U.S. Pat. No.3,442,808.

Examples of dispersants prepared from polymers prepared from metallocenecatalysts and then functionalized, derivatized, or functionalized andderivatized are described in U.S. Pat. Nos. 5,266,223, 5,128,056,5,200,103, 5,225,092, 5,151,204 and 5,334,775; WO-A-94/13709 and94/19436; and EP-A-440506, 513211 and 513157.

The functionalizations, derivatizations, and post-treatments describedin the following patents may also be adapted to functionalize and/orderivatize the preferred polymers described above: U.S. Pat. Nos.3,275,554, 3,565,804, 3,442,808, 3,442,808, 3,087,936 and 3,254,025.

3. Detergent

Metal-containing or ash-forming detergents function both as detergentsto reduce or remove deposits and as acid neutralizers or rustinhibitors, thereby reducing wear and corrosion and extending enginelife. Detergents generally comprise a polar head with a long hydrophobictail, with the polar head comprising a metal salt of an acidic organiccompound. The salts may contain a substantially stoichiometric amount ofthe metal in which case they are usually described as normal or neutralsalts, and would typically have a total base number or TBN (as may bemeasured by ASTM D2896) of from 0 to 80. It is possible to include largeamounts of a metal base by reacting an excess of a metal compound suchas an oxide or hydroxide with an acidic gas such as carbon dioxide. Theresulting overbased detergent comprises neutralised detergent as theouter layer of a metal base (e.g. carbonate) micelle. Such overbaseddetergents may have a TBN of 150 or greater, and typically of from 250to 450 or more.

Detergents that may be used include oil-soluble neutral and overbasedsulfonates, phenates, sulfurized phenates, thiophosphonates,salicylates, and naphthenates and other oil-soluble carboxylates of ametal, particularly the alkali or alkaline earth metals, e.g., sodium,potassium, lithium, calcium, and magnesium. The most commonly usedmetals are calcium and magnesium, which may both be present indetergents used in a lubricant, and mixtures of calcium and/or magnesiumwith sodium. Particularly convenient metal detergents are neutral andoverbased calcium sulfonates having TBN of from 20 to 450 TBN, andneutral and overbased calcium phenates and sulfurized phenates havingTBN of from 50 to 450.

Sulfonates may be prepared from sulfonic acids which are typicallyobtained by the sulfonation of alkyl substituted aromatic hydrocarbonssuch as those obtained from the fractionation of petroleum or by thealkylation of aromatic hydrocarbons. Examples included those obtained byalkylating benzene, toluene, xylene, naphthalene, diphenyl or theirhalogen derivatives such as chlorobenzene, chlorotoluene andchloronaphthalene. The alkylation may be carried out in the presence ofa catalyst with alkylating agents having from about 3 to more than 70carbon atoms. The alkaryl sulfonates usually contain from about 9 toabout 80 or more carbon atoms, preferably from about 16 to about 60carbon atoms per alkyl substituted aromatic moiety.

The oil soluble sulfonates or alkaryl sulfonic acids may be neutralizedwith oxides, hydroxides, alkoxides, carbonates, carboxylate, sulfides,hydrosulfides, nitrates, borates and ethers of the metal. The amount ofmetal compound is chosen having regard to the desired TBN of the finalproduct but typically ranges from about 100 to 220 wt % (preferably atleast 125 wt %) of that stoichiometrically required.

Metal salts of phenols and sulfurised phenols are prepared by reactionwith an appropriate metal compound such as an oxide or hydroxide andneutral or overbased products may be obtained by methods well known inthe art. Sulfurised phenols may be prepared by reacting a phenol withsulfur or a sulfur containing compound such as hydrogen sulfide, sulfurmonohalide or sulfur dihalide, to form products which are generallymixtures of compounds in which 2 or more phenols are bridged by sulfurcontaining bridges.

4. Antiwear and Antioxidant Agent

Dihydrocarbyl dithiophosphate metal salts are frequently used asanti-wear and antioxidant agents. The metal may be an alkali or alkalineearth metal, or aluminum, lead, tin, molybdenum, manganese, nickel orcopper. The zinc salts are most commonly used in lubricating oil inamounts of 0.1 to 10, preferably 0.2 to 2 wt. %, based upon the totalweight of the lubricating oil composition. They may be prepared inaccordance with known techniques by first forming a dihydrocarbyldithiophosphoric acid (DDPA), usually by reaction of one or more alcoholor a phenol with P₂ S₅ and then neutralizing the formed DDPA with a zinccompound. For example, a dithiophosphoric acid may be made by reactingmixtures of primary and secondary alcohols. Alternatively, multipledithiophosphoric acids can be prepared where the hydrocarbyl groups onone are entirely secondary in character and the hydrocarbyl groups onthe others are entirely primary in character. To make the zinc salt anybasic or neutral zinc compound could be used but the oxides, hydroxidesand carbonates are most generally employed. Commercial additivesfrequently contain an excess of zinc due to use of an excess of thebasic zinc compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil soluble saltsof dihydrocarbyl dithiophosphoric acids and may be represented by thefollowing formula: ##STR1## wherein R and R' may be the same ordifferent hydrocarbyl radicals containing from 1 to 18, preferably 2 to12, carbon atoms and including radicals such as alkyl, alkenyl, aryl,arylalkyl, alkaryl and cycloaliphatic radicals. Particularly preferredas R and R' groups are alkyl groups of 2 to 8 carbon atoms. Thus, theradicals may, for example, be ethyl, n-propyl, i-propyl, n-butyl,i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl,octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl,methylcyclopentyl, propenyl, butenyl. In order to obtain oil solubility,the total number of carbon atoms (i.e. R and R') in the dithiophosphoricacid will generally be about 5 or greater. The zinc dihydrocarbyldithiophosphate can therefore comprise zinc dialkyl dithiophosphates.Conveniently at least 50 (mole) % of the alcohols used to introducehydrocarbyl groups into the dithiophosphoric acids are secondaryalcohols.

Oxidation inhibitors or antioxidants reduce the tendency of mineral oilsto deteriorate in service which deterioration can be evidenced by theproducts of oxidation such as sludge and varnish-like deposits on themetal surfaces and by viscosity growth. Such oxidation inhibitorsinclude hindered phenols, alkaline earth metal salts ofalkylphenolthioesters having preferably C₅ to C₁₂ alkyl side chains,calcium nonylphenol sulfide, ashless oil soluble phenates and sulfurizedphenates, phosphosulfurized or sulfurized hydrocarbons, phosphorousesters, metal thiocarbamates, oil soluble copper compounds as describedin U.S. Pat. No. 4,867,890, and molybdenum containing compounds.

Typical oil soluble aromatic amines having at least two aromatic groupsattached directly to one amine nitrogen contain from 6 to 16 carbonatoms. The amines may contain more than two aromatic groups. Compoundshaving a total of at least three aromatic groups in which two aromaticgroups are linked by a covalent bond or by an atom or group (e.g., anoxygen or sulfur atom, or a --CO--, --SO₂ -- or alkylene group) and twoare directly attached to one amine nitrogen also considered aromaticamines. The aromatic rings are typically substituted by one or moresubstituents selected from alkyl, cycloalkyl, alkoxy, aryloxy, acyl,acylamino, hydroxy, and nitro groups.

5. Other Additives

Friction modifiers may be included to improve fuel economy. Oil-solublealkoxylated mono- and diamines are well known to improve boundary layerlubrication. The amines may be used as such or in the form of an adductor reaction product with a boron compound such as a boric oxide, boronhalide, metaborate, boric acid or a mono-, di- or trialkyl borate.

Other friction modifiers include esters formed by reacting carboxylicacids and anhydrides with alkanols. Other conventional frictionmodifiers generally consist of a polar terminal group (e.g. carboxyl orhydroxyl) covalently bonded to an oleophillic hydrocarbon chain. Estersof carboxylic acids and anhydrides with alkanols are described in U.S.Pat. No. 4,702,850. Examples of other conventional friction modifiersare described by M. Belzer in the "Journal of Tribology" (1992), Vol.114, pp. 675-682 and M. Belzer and S. Jahanmir in "Lubrication Science"(1988), Vol. 1, pp. 3-26.

Rust inhibitors selected from the group consisting of nonionicpolyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, andanionic alkyl sulfonic acids may be used.

Copper and lead bearing corrosion inhibitors may be used, but aretypically not required with the formulation of the present invention.Typically such compounds are the thiadiazole polysulfides containingfrom 5 to 50 carbon atoms, their derivatives and polymers thereof.Derivatives of 1,3,4 thiadiazoles such as those described in U.S. Pat.Nos. 2,719,125; 2,719,126; and 3,087,932; are typical. Other similarmaterials are described in U.S. Pat. Nos. 3,821,236; 3,904,537;4,097,387; 4,107,059; 4,136,043; 4,188,299; and 4,193,882. Otheradditives are the thio and polythio sulfonamides of thiadiazoles such asthose described in UK. Patent Specification No. 1,560,830.Benzotriazoles derivatives also fall within this class of additives.When these compounds are included in the lubricating composition, theyare preferrably present in an amount not exceeding 0.2 wt % activeingredient.

A small amount of a demulsifying component may be used. A preferreddemulsifying component is described in EP 330,522. It is obtained byreacting an alkylene oxide with an adduct obtained by reacting abis-epoxide with a polyhydric alcohol. The demulsifier should be used ata level not exceeding 0.1 mass % active ingredient. A treat rate of0.001 to 0.05 mass % active ingredient is convenient.

Pour point depressants, otherwise known as lube oil flow improvers,lower the minimum temperature at which the fluid will flow or can bepoured. Such additives are well known. Typical of those additives whichimprove the low temperature fluidity of the fluid are C₈ to C₁₈ dialkylfumarate/vinyl acetate copolymers and polyalkylmethacrylates.

Foam control can be provided by many compounds including an antifoamantof the polysiloxane type, for example, silicone oil or polydimethylsiloxane.

Some of the above-mentioned additives can provide a multiplicity ofeffects; thus for example, a single additive may act as adispersant-oxidation inhibitor. This approach is well known and does notrequire further elaboration.

C. Viscosity Modifiers

The viscosity modifier may be monofunctional or multifunctional.Suitable compounds for use as monofunctional viscosity modifiers aregenerally high molecular weight hydrocarbon polymers, includingpolyesters. Oil soluble viscosity modifying polymers generally haveweight average molecular weights of from about 10,000 to 1,000,000,preferably 20,000 to 500,000, which may be determined by gel permeationchromatography (as described above) or by light scattering.

Representative examples of suitable viscosity modifiers arepolyisobutylene, copolymers of ethylene and propylene and higheralpha-olefins, polymethacrylates, polyalkylmethacrylates, methacrylatecopolymers, copolymers of an unsaturated dicarboxylic acid and a vinylcompound, inter polymers of styrene and acrylic esters, and partiallyhydrogenated copolymers of styrene/isoprene, styrene/butadiene, andisoprene/butadiene, as well as the partially hydrogenated homopolymersof butadiene and isoprene and isoprene/divinylbenzene.

The multifunctional viscosity modifier may be one or more of:polymethacrylates derivatised with nitrogen containing monomers such asvinylpyridine, N-vinylpyrrolidinone, or N,N'-dimethylaminoethylmethacrylate; ethylene-propylene copolymers directly amine derivatised;hydrogenated star polymers reacted with a carboxylic acid derivative andthen reacted with an amine; hydrogenated styrene-butadiene-ethyleneoxide block copolymers; and ethylene alphaolefin copolymers solution ormelt grafted with ethylenically unsaturated a dicarboxylic acidderivative and then reacted with an amine.

A preferred multifunctional viscosity modifier comprises a derivatizedethylene-alpha olefin copolymer comprising an adduct of (i) a copolymerhaving a number average molecular weight of from 20,000 to 100,000,functionalized with mono- or dicarboxylic acid material; and (ii) atleast one amine, and in a particularly preferred aspect theethylene-alpha olefin copolymer comprises either a) from 30 to 60 weightpercent monomer units derived from ethylene and from 70 to 40 weightpercent monomer units derived from alpha-olefin, or b) from 60 to 80weight percent monomer units derived from ethylene and from 40 to 20weight percent monomer units derived from alpha olefin, or a mixture ofa) and b).

The multifunctional viscosity modifiers used in the present inventionmay be prepared by known techniques. The preferred mixture ofderivatized ethylene-alpha olefin copolymers may be prepared byfunctionalising and derivatising ethylene alpha-olefin copolymers suchas described in EP-A-616616 and WO-A-94/13763.

The viscosity modifier used in the invention will be used in an amountto give the required viscosity characteristics. Since they are typicallyused in the form of oil solutions the amount of additive employed willdepend on the concentration of polymer in the oil solution comprisingthe additive. However by way of illustration, typical oil solutions ofpolymer used as VMs are used in amount of from 1 to 30% of the blendedoil. The amount of VM as active ingredient of the oil is generally from0.01 to 6 wt %, and more preferably from 0.1 to 2 wt %.

When lubricating compositions contain one or more of the above-mentionedadditives, each additive is typically blended into the base oil in anamount which enables the additive to provide its desired function.Representative effective amounts of such additives, when used incrankcase lubricants, are listed below. All the values listed are statedas mass percent active ingredient.

    ______________________________________                                                            MASS %   MASS %                                           ADDITIVE            (Broad)  (Preferred)                                      ______________________________________                                        Ashless Dispersant  0.1-20   1-8                                              Metal detergents    0.1-15   0.2-9                                            Corrosion Inhibitor 0-5        0-1.5                                          Metal dihydrocarbyl dithiophosphate                                                               0.1-6    0.1-4                                            Anti-oxidant        0-5      0.01-2                                           Pour Point Depressant                                                                             0.01-5   0.01-1.5                                         Anti-Foaming Agent  0-5      0.001-0.15                                       Supplemental Anti-wear Agents                                                                       0-1.0    0-0.5                                          Friction Modifier   0-5        0-1.5                                          Viscosity Modifier  0.01-10  0.25-3                                           Basestock           Balance  Balance                                          ______________________________________                                    

The components may be incorporated into a base oil in any convenientway. Thus, each of the components can be added directly to the oil bydispersing or dissolving it in the oil at the desired level ofconcentration. Such blending may occur at ambient temperature or at anelevated temperature.

Preferably all the additives except for the viscosity modifier and thepour point depressant are blended into a concentrate or additive packagedescribed herein as the detergent inhibitor package, that issubsequently blended into basestock to make finished lubricant. Use ofsuch concentrates is conventional. The concentrate will typically beformulated to contain the additive(s) in proper amounts to provide thedesired concentration in the final formulation when the concentrate iscombined with a predetermined amount of base lubricant.

Preferably the detergent inhibitor package is made in accordance withthe method described in U.S. Pat. No. 4,938,880. That patent describesmaking a premix of ashless dispersant and metal detergents that ispre-blended at a temperature of at least about 100° C. Thereafter thepre-mix is cooled to at least 85° C. and the additional components areadded.

The final formulations may employ from 5 to 25 mass % and preferably 5to 18 mass %, typically about 10 to 15 mass % of the concentrate oradditive package with the remainder being base oil.

The invention will now be described by of illustration only withreference to the following examples. In the examples, unless otherwisenoted, all treat rates of all additives are reported as mass percentactive ingredient.

EXAMPLES 1 AND 2, AND COMPARATIVE EXAMPLE 3

Synthetic SAE 5W40 multigrade passenger car motor oils meeting theA.P.I. SH quality level were prepared by blending into a PAO basestock,Mobil SHF 61, an additive package with and without the use of apolyisobutenyl succinic anhydride (prepared from polyisobutene havingM_(n) of about 950 as measured by GPC), and PARATONE 8002, an olefincopolymer monofunctional viscosity modifier available form ExxonChemical Limited. The oils were tested for seal compatibility with FKM(SRE) AK6 fluorocarbon elastomer in the VW PV-334 test (dated Oct. 29,1993).

The results in the following table show that the formulations of theinvention were compatible with the seals, unlike the comparativeformulation, and yet surprisingly gave good adequate stability and goodengine performance as evidenced by the ability of the oils to meet therequirements of A.P.I. SH, despite the absence of organic acid ester inthe basestock.

                  TABLE 1                                                         ______________________________________                                        Example       1        2       3 (Comparative)                                ______________________________________                                        Additive package (mass %)                                                     basic package.sup.1                                                                         12.11    12.11   12.11                                          PIBSA.sup.2   0.25     0.5     0                                              Viscosity                                                                     modifier (mass %)                                                             PARATONE 8002 11.0     11.0    11.0                                           Mobil SHF 61  balance  balance balance to 100                                 (mass %)      to 100   to 100                                                 Elastomer compatibility                                                       Tensile strength                                                                            9.4      9.1     8.5                                            (MPa) - pass ≧ 8.0                                                     Elongation at break                                                                         199      216     188                                            (%) - pass ≧ 160                                                       Cracks - pass =                                                                             none     none    yes                                            none                                                                          ______________________________________                                         Footnotes:                                                                    .sup.1 = a detergent inhibitor package comprising ashless dispersant,         metalcontaing detergents, antioxidant, antiwear additive, antifoam            additive, demulsifier, friction modifier;                                     .sup.2 = a polyisobutenyl succinic anhydride (prepared from polyisobutene     having M.sub.n of about 950 as measured by GPC                           

I claim:
 1. A stable, multigrade synthetic lubricating oil for aninternal combustion engine, the lubricating oil having improvedcompatibility with elastomeric seals, the lubricating oil comprising:(a)a fully synthetic polyalphaolefin oligomer basestock of lubricatingviscosity substantially free of both natural oils and synthetic organicacid ester oils; (b) an additive package comprising a polybutenylsubstituted succinic acid or anhydride in which the polybutenyl grouphas a number average molecular weight (Mn) of from 700 to 5000; and (c)a hydrocarbon polymer viscosity modifier;wherein the syntheticlubricating oil is more compatible with elastomeric seals than acorresponding lubricating oil without the polybutenyl substitutedsuccinic acid or anhydride.
 2. A lubricating oil as claimed in claim 1,in which the polybutenyl substituted succinic acid or anhydride ispresent in the basestock in an amount of from 0.01 to 5 mass %.
 3. Alubricating oil as claimed in claim 2, in which the dicarboxylic acid oranhydride is present in the oil in an amount of from 0.1 to 1 mass %. 4.A lubricating oil as claimed in claim 1, in which the additive packageincludes one or more of ashless dispersant, metal detergent, corrosioninhibitor, anti-wear additive, antioxidant, pour point depressant,antifoam agent and friction modifier.
 5. A stable, multigrade syntheticlubricating oil as claimed in claim 1, wherein the polybutenylsubstituted succinic acid or anhydride is polyisobutenyl succinicanhydride in which the polyisobutenyl backbone has a Mn of from 700 to2500 and is present in the oil in an amount of from 0.01 to 5 mass %. 6.A method for providing a stable, multigrade synthetic lubricant for aninternal combustion engine and improving the compatibility of thesynthetic lubricant with elastomeric seals, which method comprisesadding to a fully synthetic polyalphaolefin basestock of lubricating oilviscosity substantially free of both natural oils and synthetic organicester oils (1) a polybutenyl substituted succinic acid or anhydride inwhich the polybutenyl group has a number average molecular weight (Mn)of from 700 to 5000 and (2) a hydrocarbon polymer viscosity modifier.